The aim of this proposal is an understanding of the mechanisms of antiviral action of interferons (IFN) at the molecular level. Since different mechanisms are apparently activated against distinct viruses, I propose to investigate how treatment with IFN prevents the replication of the following viruses: Encephalomyocarditis, reo, sindbis, vesicular stomatitis, influenza and SV40. The first two viruses were shown in preliminary experiments to promote synthesis of (2 feet-5 feet)oligo(A) and activation of an endoribonuclease in interferon treated cells. Sensitive assays to measure the (2 feet-5 feet)oligo(A) concentration and the formation of double -stranded RNA of viral origin in infected cells were developed and will be used in the present investigation. In addition, synthesis and catabolism of viral RNA in IFN-treated cells will be studied by fractionation of viral RNA by gel electrophoresis and hybridization to specific radioactive probes (Northern blot analysis). Another antiviral mechanisms which results in the synthesis of inactive viral mRNA unmethylated in the guanosine residue of the cap will also be investigated. Changes in the cellular level of S-adenosylhomocysteine may explain this IFN effect. In another line of research, the binding of iodinated IFN to cellular receptors will be studied. Interferon produced in E. coli by recombinant DNA technology will be used in these experiments, which will investigate whether IFN undergoes a temperature-dependent change after binding to cells, whether it is internalized or is released from cell receptors after the initial binding. The receptors level in cells unresponsive to IFN will be also investigated. The long-range objective of these studies is an understanding of the mechanism of action of IFN, from their interaction with receptors to the induction of the synthesis of specific enzymes and their activation in infected cells.